In recent years, memory systems comprising nonvolatile memories have become widespread. As one such memory system, a solid-state drive (SSD) comprising a NAND flash memory (hereinafter referred to as a NAND memory) is known. The SSD is used as main storage of various information processing apparatuses.
In the SSD, a controller which executes overall control over each structural element, more specifically, controls access to the NAND memory in accordance with a request from a host device, is installed. In addition, the SSD is required to operate with priority given to performance, or conversely, operate with a certain level of performance maintained during a predetermined period, even if the performance is restrained to some extent, for example, in accordance with a request (setting) of the host device. To respond to such a request, it is important to appropriately control the performance of the SSD by the controller in consideration of a life.